Dot & Cross Diagrams (Cambridge (CIE) A Level Chemistry): Flashcards

A dot and cross diagram shows the arrangement of outer-shell electrons in an ionic or covalent compound or element, using dots and crosses to represent electrons from different atoms.

1. Only outer-shell electrons are shown.

2. The ion is enclosed in square brackets to show the charge is spread across the whole ion.

3. The ionic charge is written at the top right-hand corner outside the brackets.

False. Only outer-shell (valence) electrons are shown in dot and cross diagrams.

In a dative covalent bond, one atom provides both electrons. In a displayed formula, this bond is shown by an arrow pointing away from the lone pair.

Coordinate bonding (also called dative covalent bonding) is a type of covalent bond in which one atom provides both electrons needed to form the shared pair.

The expanded octet rule applies when an atom has more than eight electrons in its outer shell. It is most commonly shown by elements in Period 3 and beyond (e.g. P, S) that have available d orbitals, such as in PCl₅ and SF₆.

False. BF₃ is an example of the incomplete octet rule — boron has only six electrons in its outer shell after forming three bonds, making it electron-deficient.

In ionic bonding, metal atoms transfer electrons to non-metal atoms. Both ions formed achieve a noble gas electron configuration.

The diagram shows four N–H bonds around a central nitrogen atom, all within square brackets with a 1+ charge. Three bonds are ordinary covalent bonds (one electron from N, one from H) and one is a dative covalent (coordinate) bond in which the nitrogen lone pair provides both electrons to bond with H⁺.